So here, finally, is a list of essential oils with warnings against using on or around childrenaccording to The Book, Essential Oil Safety (click here to download a printable pdf version of this list):

Anise/AniseedPimpinella anisum - avoid using (all routes) on children under 5

Anise (Star)Illicium verum - avoid using (all routes) on children under 5

Basil (lemon)Ocimum x citriodorum - avoid topical use on children under 2

BenzoinStyrax benzoin, Styrax paralleloneurus and Styrax tonkinensis - avoid topical use on children under 2

Birch (sweet)Betula lenta - avoid using (all routes) on children

Black SeedNigella sativa - avoid topical use on children under 2

*CajuputMelaleuca cajuputi, Melaleuca leucadendron - avoid using on children under 6

*CardamonElettaria cardamomum - avoid using (all routes) on children under 6

CassiaCinnamomum cassia, Cinnamomum aromaticum - avoid topical use on children under 2

* indicates essential oils that are high in 1,8-cineole and can potentially cause respiration to slow in children. If you are looking for age-appropriate anti-congestion suggestions, read this post: Anti-Germ and Anti-Congestion blend recipes.